It is well documented that Down Syndrome (DS) individuals demonstrate poorer auditory short-term memory, language comprehension, and hearing ability than do their non-DS mentally retarded (MR) peers. Three primary objectives of this project are: 1) to evaluate cognitive processing components that potentially underlie deficient DS auditory memory and language abilities; 2) to determine the contribution of hearing impairment to these processing difficulties; and 3) to chart developmental changes in memory and language abilities in DS adolescents. Matched samples of 35 DS and 35 MR adolescents will be seen once a year for three years in an individualized assessment session that includes experimental tasks, standardized tests, and a comprehensive audiological assessment. The standardized tests will focus on short-term memory and language ability and the audiological assessment will focus on hearing sensitivity and middle ear functioning; these tests will be repeated each year. Nonrepeated experimental tasks will also be used each year to explore two potential DS auditory processing deficiencies: speed of item identification and use of subvocal phonological coding. These experiments will determine whether distinctive performance patterns characterize DS and MR processing of words; correlations will determine whether processing patterns relate to level of hearing impairment and global measures of memory and language. Other project objectives include: a) providing a baseline data set on word perception, short-term memory, and language skills in DS adolescents prior to dementia-related decline; b) determining whether language comprehension and production follow similar developmental paths in DS adolescents; c) using an MR control group to evaluate the significance of relationships between hearing ability, short-term memory, and language functioning in DS individuals; and d) determining the developmental course of memory, language, and hearing abilities in DS individuals during adolescence. The project will yield findings that are directly relevant to psychological researchers, educators, and speech- hearing therapists interested in the developmental relationship among deficient auditory short-term memory, poor language comprehension, and hearing impairment in DS individuals.